The invention disclosed herein pertains generally to supercharged internal combustion engines, and more particularly to a method and apparatus for bypassing a portion of the air charge supplied to a supercharged internal combustion engine and diverting it to a turbocharger supplying air to the engine.
Bypass devices in supercharged internal combustion engines are used mainly in conjunction with turbochargers. Such bypass devices serve to improve the low load characteristics of supercharged internal combustion engines having elevated charge compression ratios, and are used predominantly with four stroke diesel engines which are supercharged by turbochargers. A typical bypass device includes a bypass duct which connects a charging air duct, extending downstream from the compressor of a turbocharger, to an exhaust gas duct emanating from the engine and arranged upstream from the turbine of the turbocharger. Such a bypass device typically also includes a valve arranged in the bypass duct, which valve is used to regulate the flow of air which flows from the charging air duct through the bypass duct to the turbine of the turbocharger.
By regulating the flow of air diverted from the charging air duct through the bypass duct to the turbocharger, it is possible to match the absorption capacity of the engine to the characteristics of the compressor so that a higher supercharging pressure is obtained at low loads. At maximum or full load the bypass duct is closed. Between the starting point of the engine and the full load point, the bypass valve is progressively opened as the difference between the absorption capacity of the engine and the compressor's pumping limit or the air/fuel ratio decreases. It is common practice to utilize the pressures upstream and downstream of the bypass duct, the engine speed, and the gas temperature upstream of the turbine as the variables and parameters used in controlling the bypass valve.
If the pressure gradient across the bypass duct becomes too small to enable air to flow through the bypass duct, it is possible to use heat exchangers, auxiliary combustion chambers arranged upstream of the turbine, or other means for supplying compressed air to the turbocharger. It is also known to utilize the pulsation energy of the engine exhaust gases to promote the flow of bypass air to the turbocharger. Engines with these known supplemental devices generally have satisfactory acceleration and low load characteristics, but are costly because of the expenses involved in construction.
A primary object of the present invention is to provide a method and apparatus for regulating the flow of bypass air through a bypass duct of a turbocharged internal combustion engine, which method and apparatus employ pressure pulsations produced by the periodic, alternating charging of the internal combustion engine to excite periodic pressure differences across the bypass duct, to produce an increased flow of charging air through the bypass duct.
Another object of the present invention is to provide a method and apparatus for regulating the flow of bypass air through a bypass duct of a turbocharged internal combustion engine without the use of supplemental devices.
Apparatus for regulating a flow of air through a bypass duct of a turbocharged internal combustion engine, according to a preferred embodiment of the present invention, includes a turbocharger and a six-cylinder internal combustion engine. A turbine of the turbocharger drives a compressor which supplies compressed air to the engine through a charging air duct. The charging air duct feeds compressed air from the compressor to an air receiver, which air receiver acts as a damping volume. The air receiver in turn feeds air into two air oscillation pipes, each of which pipes feeds air to one of two inlet manifolds. Each of the inlet manifolds supplies air to three cylinders of the six-cylinder engine through three suction pipes.
Six exhaust pipes feed exhaust gases from the cylinders of the six-cylinder engine to an exhaust gas manifold. In addition, two bypass ducts feed compressed air from the inlet manifolds to the exhaust gas manifold. A bypass valve and a non-return valve, which non-return valve prevents backflow, are arranged in each bypass duct, and are used to regulate the flow of compressed air through each bypass duct.
During the operation of the engine, the periodic downstroke of the piston in each cylinder produces a periodic suction effect which results in periodic pressure fluctuations propagating into the suction pipes connecting the two inlet manifolds to the engine cylinders. These pressure fluctuations propagate through each of the inlet manifolds and into each of the air oscillation pipes. The natural frequency of the column of air in each air oscillation pipe corresponds to the suction pulsation frequency of the engine in the engine speed range in which a maximum bypass flow rate is required. Thus, the air columns in the air oscillation pipes resonate in this speed range, resulting in the pressure differences across the bypass ducts reaching a maximum value, and the bypass flow rate thereby also reaching a maximum value.